The present invention generally relates to complementary metal oxide semiconductor (CMOS) field effect transistor (FET) devices, and more particularly, to voltage push pull driver output stages with dynamic voltage switching.
Current CMOS technology may utilize 1.5V power supplies due to device scaling and power saving. The 1.5V power supply devices have a lower breakdown threshold voltage relative to, for example, 1.8V power supply devices. However, the devices utilizing a 1.5V power supply may provide increased performance due to having a lower voltage supply.
Reliability breakdown may include a gate dielectric oxide breakdown and parasitic bipolar breakdown occurring as a result of exceeding a device breakdown threshold voltage. Such limitations associated with lower power supply voltage devices, such as 1.5V FETs, may present challenges in using 1.5V FET CMOS devices in supporting legacy 3.3V LVTTL CMOS designs within a single circuit.
A 3.3V push pull driver output stage may require the stacking of two 1.8V CMOS p-channel field effect transistor (PFET) for a voltage pull up and two 1.8V CMOS n-channel field effect transistor (NFET) for a voltage pull down. Each of these 1.8V CMOS FET has a dielectric breakdown voltage of about 1.95V as opposed to a lower 1.6V breakdown voltage for a 1.5V CMOS device. However, a two device stacking topology may no longer be supported by 1.5V CMOS devices. This may occur as a result of the 1.5V CMOS devices having a substantially lower breakdown voltage and, therefore, being more susceptible to damage.